The U.S. Department of Transportation (DOT) 4-hour rule is a consumer protection regulation specifically targeting "tarmac delays" for international flights. Under this rule, airlines operating at U.S. airports are prohibited from keeping passengers on an aircraft for more than 4 hours during a delay on the tarmac (either before departure or after landing) without providing an opportunity to deplane. For domestic flights, the limit is even shorter at 3 hours. There are only two exceptions to this rule: if the pilot determines that returning to the gate would pose a safety or security risk, or if Air Traffic Control advises that doing so would significantly disrupt airport operations. While the "hard limit" is 4 hours, the airline has additional obligations during the wait: they must provide food and water no later than 2 hours into the delay, ensure that toilets remain functional, and provide adequate medical attention if needed. If an airline violates these time limits without a valid safety reason, they can face massive fines—often tens of thousands of dollars per passenger—making it a powerful deterrent against lengthy "gate-holding" situations.